Method for providing a hermetically sealed coin cell

ABSTRACT

A hermetically sealed coin cell is described. The coin cell has the opposite polarity terminals isolated from one another by a glass-to-metal seal. Glassing a conductive disc inside a ring of greater diameter and height forms this seal. The height of the ring is equivalent to the desired height of the cell. The disc acts as one cell terminal, which can be positive or negative, and the ring serves as the other terminal. In plan view, both terminals are on the same side of the cell. This allows for easy mounting and connection to an electronic circuit board, and the like.

This application is a divisional of U.S. Ser. No. 10/761,037, filed Jan.20, 2004 which also claims the Provisional Application No. 60/441,015,filed Jan. 17, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to the conversion of chemicalenergy to electrical energy. More particularly, the present inventionrelates to a hermetically sealed coin-type cell. The cell is of either aprimary or a secondary chemistry.

2. Prior Art

Implantable electrochemical cells are in widespread use. These cells arehermetically sealed using an insulating glass to separate the terminalpin from the case. Power sources of this type prevent internalcomponents, such as the electrolyte, from coming into contact with bodytissue or sensitive electrical components of the associated implantablemedical device. These cells are easily manufactured in large sizes.However, as cell size becomes smaller, it becomes increasingly morecomplicated to perform the required welding and fabrication processes.

Often, coin cells are used in applications that require a very smallpower source. A top and bottom terminal crimped together with aninsulating gasket characterized coin cells. Contact between theelectrodes and their current collectors are achieved by using stackpressure, which eliminates the need for welding the electrodes to theterminals. Also, since the number of parts is relatively small in a coincell, this minimizes the need for many manufacturing operations. Theproblem with coin cells is, however, that the insulating gasket istypically of a polymeric or plastic material. Plastics are porous and donot constitute a hermetic seal. Also, these seals are unreliable andprone to leaking. As such, coin cells of the prior art are not suitablefor implantable applications.

SUMMARY OF THE INVENTION

The present invention coin cell is distinguishable from those of theprior art in that the opposite polarity terminals are isolated from oneanother using a glass-to-metal seal. Glassing a conductive disc inside aring of greater diameter and height forms this seal. The height of thering is equivalent to the desired height of the cell. The disc acts asone cell terminal, which can be positive or negative, and the ringserves as the other terminal. In plan view, both terminals are on thesame side of the cell. This allows for easy mounting and connection toan electronic circuit board, and the like.

These and other aspects of the present invention will become moreapparent to those of ordinary skill on the art by reference to thefollowing description and the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of the coin cell 10 of the present invention.

FIG. 2 is a bottom plan view of the coin cell 10 shown in FIG. 1.

FIG. 3 is a cross-sectional view along line 3—3 of FIG. 1.

FIG. 4 is a cross-sectional view of the ring 12 and disc 14 for the coincell 10.

FIG. 5 is a cross-sectional view showing the insulative glass 20 sealingbetween the ring 12 and disc 14 of FIG. 4.

FIG. 6 is a cross-sectional view showing the positioning of the firstand second electrodes 22 and 26 of the coin cell of FIG. 5.

FIG. 7 is a cross-sectional view showing the electrolyte 28 activatingthe electrodes 22, 26 of FIG. 6.

FIG. 8 is a cross-sectional view showing the plate 30 closing the coincell of FIG. 7.

FIG. 9 is a schematic showing a laser 32 welding the plate 30 to thering 12 to hermetically close the coin cell of FIG. 8.

FIG. 10 is a cross-sectional view showing an alternate embodiment of acoin cell 100 according to the present invention.

FIG. 11 is a cross-sectional view showing another embodiment of a coincell 10A having a spring 36 captured between the second electrode 26 andlid 30 to provide stack pressure for the electrode assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, FIGS. 1 to 9 illustrate a coin cell 10according to the present invention. The coin cell 10 comprises acylindrically shaped ring 12 surrounding a circular disc 14. The ring 12has a cylindrical outer wall 12A that is coaxial with a cylindricalinner wall 12B. The outer and inner walls 12A, 12B of the ring 12 extendto and meet with a spaced apart and perpendicularly oriented bottom orlower end 12C and a top or upper end 12D. The upper end 12D includes anannular step 16 adjacent to the inner wall 12B.

The disc 14 serves as a base for one of the electrodes and comprises acylindrically shaped outer wall 14A extending to a perpendicularlyoriented bottom or lower end 14B and a top or upper end 14C. A circularrecess 18 is provided in the disc. The recess 18 comprises a cylindricalinner wall 14D extending to an inner bottom wall 14E. The disc lower end14B and the inner lower wall 14E are parallel to each other. Further,the outer and inner cylindrical walls 14A, 14D are coaxial. The heightof the inner wall 14D is from about 10% to about 90% of that of theouter wall 14A. This means that the thickness of the disc between thelower end 14B and the inner lower wall 14E is from about 10% to about90% of the height of the outer wall 14A.

The disc 14 is sized to fit inside the ring 12. As showin in FIGS. 3 to9, with the ring lower end 12C aligned coplanar with the disc lower end14B, the disc upper end 14C is spaced from and below the ring upper end12D. With the disc in a coaxial relationship with the ring, the discouter wall 14A is spaced from the ring inner wall 12B. An insulativeglass 20 is sealed in an annular manner between the ring inner wall 12Band the disc outer wall 14A (FIG. 5). This serves to hermetically sealthe disc to the ring.

A first electrode 22 of an electrode active material is nested in therecess 18. The first electrode comprises spaced apart upper and lowermajor sides. The upper electrode side is shown substantially coplanarwith the disc upper end 14C; however, this is not necessary. Theelectrode upper side can be spaced above disc upper end 14C, if desired.

An insulating separator 24 resting on the disc upper end 14C spans theentire area surrounded by the ring inner wall 12B. A second electrode 26of an opposite polarity as the first electrode is then positioned on theopposite side of the separator 24.

As previously discussed, the coin cell 10 is of either a primarychemistry or a secondary, rechargeable chemistry. However, the coin cellwill be described with respect to the second electrode 26 being theanode or negative electrode and the first electrode 22 being the cathodeor positive electrode. For both the primary and secondary types, theanode active metal of the second electrode 26 is selected from GroupsIA, IIA and IIIB of the Periodic Table of the Elements, includinglithium, sodium, potassium, etc., and their alloys and intermetalliccompounds including, for example, Li—Si, Li—Al, Li—B, Li—Mg, and Li—Si—Balloys. The preferred metal comprises lithium. An alternate negativeelectrode comprises a lithium alloy, such as lithium-aluminum alloy. Thegreater the amounts of aluminum present by weight in the alloy, however,the lower the energy density of the cell.

For a primary coin cell, the anode 26 is a thin metal sheet or foil orpellet of the lithium material. In secondary electrochemical systems,the anode or negative electrode comprises an anode material capable ofintercalating and de-intercalating the anode active material, such asthe preferred alkali metal lighium. A carbonaceous negative electrodecomprising any of the various forms of carbon (e.g., coke, graphite,acetylene black, carbon black, glassy carbon, etc.), which are capableof reversibly retaining the lithium speciies, is preferred. A “hairycarbon” material is particularly preferred due to its relatively highlithium-retention capacity. “Hairy carbon” is a material described inU.S. Pat. No. 5,443,928 to Takeuchi et al. This patent is assigned tothe assignee of the present invention and incorporated herein byreference. Graphite is another preferred material. Regardless of theform of the carbon, fibers of the carbonaceous material are particularlyadvantageous because they have excellent mechanical properties, whichpermit them to be fabricated into rigid electrodes that are capable ofwithstanding degradation during repeated charge/discharge cycling.Moreover, the high surface area of carbon fibers allows for rapidcharge/discharge rates.

A typical negative electrode for a secondary cell is fabricated bymixing about 90 to 97 weight percent of a binder material, which ispreferably a fluoro-resin powder such as polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVDF), polyethylenetetrafluoroethylene (ETFE),polyamides, polyimides, and mixtures thereof.

In either the primary or secondary system, the reaction at the positiveelectrode 22 involves conversion of ions, which migrate from thenegative electrode 26 to the positive electrode into atomic or molecularforms. For a primary cell, the cathode active material comprises acarbonaceous chemistry or at least a first transition metal chalcogenideconstituent which may be a metal, a metal oxide, or a mixed metal oxidecomprising at least a first and a second metals or their oxides, andpossibly a third metal or metal oxide, or a mixture of a first and asecond metals or their metal oxides incorporated in the matrix of a hostmetal oxide. The cathode active material may also comprise a metalsulfide.

Carbonaceous active materials are preferably prepared from carbon andfluorine, which includes graphitic and nongraphitic forms of carbon,such as coke, charcoal or activated carbon. Fluorinated carbon isrepresented by the formula (CF_(x))_(n), wherein x varies between about0.1 to 1.9 and preferably between about 0.5 and 1.2, and (C₂F)_(n),wherein n refers to the number of monomer units, which can vary widely.

The metal oxide or the mixed metal oxide is produced by the chemicaladdition, reaction, or otherwise intimate contact of various metaloxides, metal sulfides and/or metal elements, preferably during thermaltreatment, sol-gel formation, chemical vapor deposition or hydrothermalsynthesis in mixed states. The active materials thereby produced containmetals, oxides and sulfides of Groups IB, IIB, IIIB, IVB, VB, VIIB, VIIBand VIII, which include the noble metals and/or other oxide and sulfidecompounds. A preferred cathode active material is a reaction product ofat least silver and vanadium.

One preferred mixed metal oxide has the general formula SM_(x)V₂O_(y)where SM is a metal selected from Groups IB to VIIB and VIII of thePeriodic Table of the Elements, and wherein x is about 0.30 to 2.0 and yis about 4.5 to 6.0 in the general formula. One exemplary cathode activematerial comprises silver vanadium oxide having the general formulaAg_(x)V₂O_(y) in any one of its many phases, i.e., β-phase silvervanadium oxide having in the general formula x=0.35 and y=5.8, γ-phasesilver vanadium oxide having in the general formula x=0.80 and y=5.40and ⊖-phase silver vanadium oxide having in the general formula x=1.0and y=5.5, and combination and mixtures of phases thereof. For a moredetailed description of such cathode active materials reference is madeto U.S. Pat. No. 4,310,609 to Liang et al. This patent is assigned tothe assignee of the present invention and incorporated herein byreference.

Another preferred composite cathode active material for primary cellshas the general formula Cu_(x)Ag_(y)V₂O_(z), (CSVO) and the range ofmaterial compositions is preferably about 0.01≦x≦1.0, about 0.01≦y≧1.0and about 5.01≦z≦6.5. For a more detailed description of this cathodeactive material, reference is made to U.S. Pat. No. 5,472,810 toTakeuchi et al. and U.S. Pat. No. 5,516,340 to Takeuchi et al., both ofwhich are assigned to the assignee of the present invention andincorporated herein by reference.

In addition to the previously described fluorinated carbon, silvervanadium oxide and copper silver vanadium oxide, Ag₂O, Ag₂O₂, CuF₂,Ag₂CrO₄, MnO₂, V₂O₅, MnO₂, TiS₂, Cu₂S, FeS, FeS₂, copper oxide, coppervanadium oxide, and mixtures thereof are contemplated as useful activematerials.

In secondary coin cell, the positive electrode 22 preferably comprises alithiated material that is stable in air and readily handled. Examplesof such air-stable lithiated cathode active materials include oxides,sulfides, selenides, and tellurides of such metals as vanadium,titanium, chromium, copper, molybdenum, niobium, iron, nickel, cobaltand manganese. The more preferred oxides include LiNiO₂, LiMn₂O₄,LiCoO₂, LiCO_(00.92)Sn_(0.08)O₂ and LiCo_(1-x)Ni_(x)O₂.

To charge such secondary coin cells, lithium ions comprising thepositive electrode 22 are intercalated into the carbonaceous negativeelectrode 26 by applying an externally generated electrical potential tothe cell. The applied recharging electrical potential serves to drawlithium ions from the cathode active material, through the electrolyteand into the carbonaceous material of the negative electrode to saturatethe carbon. The resulting LixC₆ negative electrode can have an x rangingfrom 0.1 to 1.0. The cell is then provided with an electrical potentialand is discharged in a normal manner.

An alternate secondary cell construction comprises intercalating thecarbonaceous material with the active lithium material before thenegative electrode is incorporated into the cell. In this case, thepositive electrode body can be solid and comprise, but not be limitedto, such active materials as manganese dioxide, silver vanadium oxide,titanium disulfide, copper oxide, copper sulfide, iron sulfide, irondisulfide and fluorinated carbon. However, this approach is comprised byproblems associated with handling lithiated carbon outside of the cell.Lithiated carbon tends to react when contacted by air or water.

The above described cathode active materials, whether of a primary or asecondary chemistry, are formed into an electrode body for incorporationinto a coin cell by mixing one or more of them with a binder material.Suitable binders are powdered fluoro-polymers; more preferably powderedpolytetrafluoroethylene or powdered polyvinylidene fluoride present atabout 1 to about 5 weight percent of the cathode mixture. Further, up toabout 10 weight percent of a conductive diluent is preferably added tothe cathode mixture to improve conductivity. Suitable materials for thispurpose include acetylene black, carbon black and/or graphite or ametallic powder such as powdered nickel, aluminum, titanium andstainless steel. The preferred cathode active mixture thus includes apowdered fluoro-polymer binder present at about 1 to 5 weight percentand about 90 to 98 weight percent of the cathode active material.

Whether the coin cell 10 is constructed as a primary or secondaryelectrochemical system, the separator 24 physically segregates the anode26 and cathode active materials 22. The separator is of an electricallyinsulative material to prevent an internal electrical short circuitbetween the electrodes, and also is chemically unreactive with the anodeand cathode active materials and both chemically unreactive with aninsoluble in the electrolyte. In addition, the separator material has adegree of porosity sufficient to allow flow there through of theelectrolyte during the electrochemical reaction of the cell. The form ofthe separator typically is a sheet placed between the anode and cathodeelectrodes. Illustrative separator materials include fabrics woven fromfluoropolymeric fibers including polyvinylidine fluoride,polyethylenetetrafluoroethylene, and polyethylenechlorotrifluoroethyleneused either alone or laminated with a fluoropolymeric microporous film,non-woven glass, polypropylene, polyethylene, glass fiber materials,ceramics, a polytetrafluoroethylene membrane commercially availableunder the designation ZITEX (Chemplast Inc.), a polypropylene membranecommercially available under the designation CELGARD (Celanese PlasticCompany Inc.), and a membrane commercially available under thedesignation DEXIGLAS (C.H. Dexter, Div., Dexter Corp.).

After the electrodes 22, 26 are housed in the ring/disc assembly, anelectrolyte 28 is filled therein. The electrolyte is provided into thedisc recess 18 and the ring 12 in an amount substantially level with thestep 16 meeting the ring inner wall 12B. Suitable nonaqueouselectrolytes comprising an inorganic salt dissolved in a nonaqueoussolvent, and more preferably an alkali metal salt dissolved in a mixtureof aprotic organic solvents comprising a low viscosity solvent includingorganic esters, ethers and dialkyl carbonates, and mixtures thereof, anda high permittivity solvent including cyclic carbonates, cyclic estersand cyclic amides, and mixtures thereof. Suitable nonaqueous solventsare substantially inert ot the anode and cathode electrode materials andpreferred low viscosity solvents include tetrahydrofuran (THF), methylacetate (MA), diglyme, triglyme, tetraglyme, dimethy carbonate (DMC),diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl ethylcarbonate (MEC), methyl propyl carbonate (MPC), ethyl propyl carbonate(EPC), 1,2-Dimethoxyethane (DME), and mixtures thereof. Preferred highpermittivity solvents include propylene carbonate (PC), thylenecarbonate (EC), butylenes carbonate (BC), acetonitrile, dimethylsulfoxide, dimethyl formamide, dimethyl acetamide, γ-butyrolactone(GBL), γ-valerolactone, N-methyl-pyrrolidinone (NMP), and mixturesthereof.

Known lithium salts that are useful as a vehicle for transport of alkalimetal ions from the anode to the cathode, and back again include LiPF₆,LiBF₄, LiAsF₆, LiSbF₆, LiClO₄, LiAlCl₄, LiGaCl₄, LiC(SO₂CF₃)₃, LiO₂,LiNO₃, LiO₂CCF₃, LiN(SO₂CF₃)₂, LiSCN, LiO₃SCF₂CF₃, LiC₆F₅SO₃, LiO₂CF₃,LiSO₃F, LiB(C₆H₅)₄, LiCF₃SO₃, and mixtures thereof. Suitable saltconcentrations typically range between about 0.8 to 1.5 molar.

A preferred electrolyte for a secondary cell of an exemplary carbonCiCoO₂ couple comprises a solvent mixture of EC:DMC:EMC:DEC. Mostpreferred volume percent ranges for the various carbonate solventsinclude EC in the range of about 20% to about 50%; DMC in the range ofabout 122% to about 75%; EMC in the range of about 5% to about 45%; andDEC in the range of about 3% to about 45%. In a preferred form of thecoin cell 10, the electrolyte is at equilibrium with respect to theratio of DMC:EMC:DEC. This is important to maintain consistent andreliable cycling characteristics. It is known that due to the presenceof low-potential (anode) materials in a charged cell, andun-equilibrated mixture of DMC:DEC in the presence of lithiated graphite(LiC₆˜0.01 V vs. Li/Li⁺) results in a substantial amount of EMC beingformed. When the concentrations of DMC, DEC and EMC change, the cyclingcharacteristics and temperature rating of the cell also changes. Suchunpredictability is unacceptable. This phenomenon is described in detailin U.S. patent application Ser. No. 10/232,166, filed Aug. 30, 2002,which is assigned to the assignee of the present invention andincorporated herein by reference. Electrolytes containing the quaternarycarbonate mixture of the present invention exhibit freezing points below−50° C., and lithium ion secondary cells activated with such mixtureshave very good cycling behavior at room temperature as well as very gooddischarge and charge/discharge cycling behavior at temperatures below−40° C.

A circular plate serving as a lid 30 is then fitted into the step 16.The lid is of a size and thickness to rest on the step with its uppersurface 30A coplanar with the ring upper end 12D. Next, the cell 10 ishermetically sealed closed by securing the lid 30 to the ring 12. Thisis done by any one of a number of methods including soldering andwelding. If the later technique is used, a laser 32 provides the weld 34between the ring 12 and the lid 30, as shown in FIG. 9. Preferably, thecell is set in a heat-sinking fixture (not shown) during welding tominimize heating of the cell components.

After the lid 30 is welded in place, a compressive force is applied tothe center of the lid. In that manner, the lid compresses the electrodematerials 22, 26 housed inside cell. The resulting stack pressure isillustrated in the completed cell of FIG. 3 where the first and secondelectrode 22, 26 are in a tightly fitting relationship captured betweenthe disc inner lower wall of 14E and the lid 30.

An important aspect of the present coin cell is the materials ofconstruction for the ring 12, disc 14, glass 20 and lid 30. Theselection of materials for these parts is critical as they must becompatible with the chemistry and potential expected in the cell toprevent possible corrosion. Also, the ring 12, disc 14 and glass 20 mustbe capable of forming a hermetic glass-to-metal seal. A compression sealis typically used to provide the reliability required for an implantableapplication. In such a seal, the coefficient of thermal expansion of thering 12 is greater than that of the glass 20, which, in turn, is greaterthan that of the disc 14. When the first electrode 22 is the cathode andthe second electrode 26 is the anode, suitable exemplary materials forthee disc 14 are titanium, and molybdenum, and alloys thereof, whichhave a relatively low coefficient of linear expansion. Stainless steel,which has a high coefficient of linear expansion, is suitable for thering 12 and lid 30. If desired, these metal parts are coated with asecondary metal or carbon to provide compatibility with the desiredelectrochemical system.

It is also contemplated by the scope of the present invention that thefirst electrode 22 is the anode and the second electrode 26 is thecathode. In that case, nickel, titanium, and molybdenum, and alloysthereof are a suitable material for the disc 14 while stainless steel issuitable for the ring 12 and lid 30.

FIG. 10 shows an alternate embodiment of a coin cell 100 according tothe present invention. The coin cell 100 comprises a cylindricallyshaped ring 112 surrounding a circular disc 114. The ring 112 has acylindrical outer wall 112A coaxial with a cylindrical inner wall 112B.The outer and inner walls 112A, 112B extend to and meet with spacedapart perpendicularly oriented lower and upper ends 112C and 112D.

The disc 114 comprises a cylindrically shaped outer wall 114A extendingto perpendicularly oriented outer lower end 114B and upper end 114C. Thedisc 114 is sized to fit inside the ring 112. With the ring lower end112C aligned coplanar with the disc lower end 114B, the disc upper end114A is spaced from the ring inner wall 112B. An insulative glass 116 issealed in an annular manner between the ring inner wall 112B and thedisc outer wall 114A. This serves to hermetically seal the disc to thering.

A first electrode 118 of an electrode active material is positioned onthe disc upper end 114C. A ring 120 of an insulative material surroundsthe first electrode. An insulating separator 122 spans the entire areasurrounded by the ring inner wall 112B. A second electrode 124 of anopposite polarity as the first electrode is then positioned on theopposite side of the separator 122. Preferably, the insulative ring 120and the separator 122 are of one of the polymeric materials previouslydescribed as being suitable for the separator 24 of coin cell 10. Anelectrolyte 126 is provided in the cavity formed by the disc 114 glassedto the ring 112. Then, a lid 128 secured to the ring upper end 112D byweld 130 completes the cell 110.

An alternative embodiment of the present coin cell 10A is shown in FIG.11 having a spring 36 captured between the second electrode 26 and thelid 30 to provide stack pressure. The spring 36 is preferably of aBelleville type having its small diameter biasing against the secondelectrode 26 and its large diameter biasing against the lid 30. Thisspring orientation applies an axial stack pressure to the electrodes 22,26 that helps promote complete and efficient discharge. If desired, awave spring (not shown) can be used instead of the Belleville spring.

Thus, it is apparent that various embodiments of hermetically sealedcoin cells of both a primary and a secondary chemistry have beendescribed. Such cells have many applications where a power source of arelatively small size is desirable. However, a particularly preferredapplication is powering an implantable medical devices, such as acardiac pacemaker, defibrillator, neurostimulator, and the like. Thesedevices require a long life, hermetically sealed power source. Thepresent coin cells 10, 10A and 100 fulfill this requirement.

It is appreciated that various modifications to the present inventiveconcepts described herein may be apparent to those of ordinary skill inthe art without departing from the scope of the present invention asdefined by the herein appended claims.

1. A method for providing an electrochemical battery, comprising thesteps of: a) providing a ring having a surrounding ring sidewallextending to a ring upper end and a ring lower end; b) providing a basehaving a surrounding base sidewall extending to a base upper end and abase lower end; c) positioning the base inside the ring surrounding thebase with the base upper end spaced below the ring upper end; d) sealingthe base to the ring with a glass material; e) positioning a firstelectrode on the base upper end, the first electrode having spaced apartupper and lower first electrode sides with the first lower electrodeside proximate the base upper end and the first upper electrode sidespaced below the ring upper end; f) supporting a separator on the firstupper electrode side; g) positioning a second, counter electrode on theseparator, the second electrode having spaced apart upper and lowersecond electrode sides with the second upper electrode side spaced belowthe ring upper end; h) activating the first and second electrodes withan electrolyte; and i) sealing a plate to the ring upper end.
 2. Themethod of claim 1 including providing the base having a recess andnesting the first electrode into the recess.
 3. The method of claim 2including providing the upper end of the first electrode being eithersubstantially coplanar with the base upper end or being spaced above thebase upper end with the first electrode nested in the base recess. 4.The method of claim 1 including having the plate applying a stackpressure to the first and second electrodes.
 5. The method of claim 1including applying stack pressure to the first and second electrodeswith a spring biasing between the plate and the second electrode.
 6. Themethod of claim 1 including providing the ring lower end and the baselower end being coplanar.
 7. The method of claim 1 including providingthe ring upper end comprising a step receiving the plate welded to thering.
 8. The method of claim 1 including surrounding the first electrodewith an insulative ring.
 9. The method of claim 1 including providingthe cell of either a primary or a secondary chemistry powering animplantable medical device.
 10. The method of claim 1 includingproviding the first electrode as a cathode of a cathode active materialcapable of intercalating or intercalating and deintercalating lithiumand the second electrode as an anode comprised of lithium or an anodeactive material capable of intercalating and deintercalating lithium.11. The method of claim 1 including providing a first coefficient ofthermal expansion of the ring being greater than a second coefficient ofthermal expansion of the glass, which, in turn, is greater than a thirdcoefficient of thermal expansion of the base.
 12. The method of claim 1including selecting the base from the group consisting of nickel,titanium, molybdenum, and alloys thereof, and proving the ring and lidbeing of stainless steel.